1. Field of the Invention
This invention is in the field of sights for hunting bows, especially laser sights.
2. Description of Prior Art
Laser sights are available for hunting bows, as shown in the prior patent discussed below. However, they lack features provided by the present invention. Simple laser pointers with beam direction adjustments are available, but each setting only applies to a specific target distance and angle of the bow. The curvature of an arrow's trajectory depends on the vertical angle of the shot--the higher the shot, the greater its curvature. Bow hunters commonly shoot from platforms about 3-9 m (10-30 ft) high in trees. From this position, the angle of a shot is normally about 20-60 degrees downward from horizontal. The bow angle and distance to a target are closely related, especially on flat terrain. Thus a bow sight can theoretically compensate for changes in the distance based on the angle of the bow, as detected by a pendulum.
U.S. Pat. No. 5,782,002 (Reed) discloses a "Laser Guidance Means", comprising a pivotally mounted laser pointer 46 that rests on an offset cylindrical cam 52. The cam is mounted on a pendulum 60. The cam is attached to the pendulum by a screw 54 that moves the cam vertically for vertical adjustment of the laser beam. However, any vertical adjustment also changes the eccentricity of the cam from its pivot point 66. This dependency is undesirable. In Reed's patent drawings, the cam is offset upward from the pivot point 66, so its apex is the top of the cam. This is counterproductive. When the bow is aimed horizontally as in FIG. 5, Reed's laser will be aimed highest relative to the bow, but the arrow will fall lowest due to the longer flight distance and maximum gravity effect on the trajectory. Thus the setting shown in Reed will compensate in the opposite direction to what is needed, making it less accurate than a fixed laser pointer. Reed's cam can be moved lower, so that its geometric center is below the pendulum pivot axis. Then it will compensate in the right direction, but the magnitude and rate of compensation is dependent on the vertical setting. For example, when the required vertical setting places the geometric center of the cam coincident with the pendulum pivot axis, the cam eccentricity is zero, eliminating compensation entirely. There is no way in Reed to maintain a correct cam offset independently of the vertical setting.
In daylight a laser spot is hard to find when sighting. It is only a small dim spot distantly reflected by the camouflage colors of nature among dapples of sunlight. In a pendulum-compensated sight, the laser spot is not along a fixed line, so a simple mechanical peep sight is not sufficient to find it. Thus a peep sight that follows the moving laser spot is needed.